RE: Long-term Safety of Pregnancy Following Breast Cancer According to Estrogen Receptor Status

We read the article by Lambertini et al. with great interest (1). This case–control study showed that, at a median follow-up of 7.2 years for women with a history of estrogen receptor (ER)–positive or ER-negative breast cancer (BC), there was no difference in disease-free survival between women who became pregnant and those who did not. Overall survival (OS) of the ER-positive patients was unaffected by pregnancy (hazard ratio [HR] = 0.84, 95% confidence interval [CI] = 0.60 to 1.18, P = .32), but, surprisingly, ER-negative patients who became pregnant had a longer median survival than those who did not (HR = 0.57, 95% CI = 0.36 to 0.90, P = .01). While these results appear reassuring to the many young BC survivors who so desperately wish to become pregnant, we are concerned about a possible source of bias that would be almost impossible to eliminate in a retrospective study of this nature.

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